Carlo Ricciardi

A biofunctional polymeric coating for microcantilever molecular recognition

An innovative route to activate silicon microcantilevers (MCs) for label free molecular recognition is presented. The method consists in coating the underivatized MCs with a functional ter-polymer based on N,N-dimethylacrylamide (DMA) bearing N-acryloyloxysuccinimide (NAS) and 3-(trimethoxysilyl)propyl-methacrylate (MAPS), two functional monomers that confer to the polymer the ability to react with nucleophilic species on biomolecules and with glass silanols, respectively. The polymer was deposited onto MCs by dip coating. Polymer coated MCs were tested in both static and dynamic modes of actuation, featuring detection of DNA hybridization as well as protein/protein interaction. In the dynamic experiments, focused on protein detection, the MCs showed an average mass responsivity of 0.4 Hz/pg for the first resonant mode and of 2.5 Hz/pg for the second resonant mode. The results of the static experiments, dedicated to DNA hybridization detection, allowed for direct estimation of the DNA duplex formation energetics, which resulted fully consistent with the nominal expected values. These results, together with easiness and cheapness, high versatility, and excellent stability of the recognition signal, make the presented route a reliable alternative to standard SAM functionalization (for microcantilevers (MCs) and for micro-electro-mechanical systems (MEMS) in general).

Polymeric mask protection for alternative KOH silicon wet etching

A new cost-effective setup for silicon bulk micromachining is presented which makes use of a polymeric protective coating, ProTEK® B2 coating, instead of a conventional hardmask. Different concentrations of KOH and bath conditions (pure, with surfactant, with stirrer, with both surfactant and stirrer) have been considered. ProTEK® B2 coating exhibits good adhesion to Si substrates, no degradation, etching rates and surface roughness comparable to literature data, and etching times greater than 180 min without damaging front side microstructures. Microcantilevers have also been fabricated using two different process flows in order to demonstrate the suitability of such a protective coating in microelectromechanical system (MEMS) technology.

Defect characterization of 4H-SiC wafers for power electronic device applications

Silicon carbide is a semiconductor of choice for the fabrication of high-power, high-temperature and high-frequency electronic devices. Nevertheless, such a material still presents many problems as regards the crystallographic quality and the presence of defects, which influence the device performance. We have investigated 4H-SiC wafers and 4H-SiC epitaxial layers by microscopy and structural techniques in order to obtain information about the defect morphology. The goal of this analysis will be to correlate them with the electrical properties of SiC for power electronic device applications.

Memristive behaviour in inkjet printed graphene oxide thin layers

Memristors are passive two-terminal memory devices predicted to have a tremendous impact on many research fields and common applications, paving the way to adaptive electronics and high computing systems. We report on a metal/insulator/metal memristor based on a graphene oxide layer, deposited by inkjet printing at room temperature. The electrical characterization of devices, showing hysteretic characteristics typical of bipolar memristive switching, are discussed and correlated to the structural and compositional analysis of the materials. The electroforming process is ascribed to a lowering in contact resistance due to carbon diffusion in Ag electrode, while the oxygen ion drift is identified as the main physical mechanism for Ag/GO/ITO resistive switching.

Two-Photon Polymerization Lithography and Laser Doppler Vibrometry of a SU-8-Based Suspended Microchannel Resonator

We present the optical realization and characterization of complex suspended microchannel resonator (SMR) for biomechanical sensing applications. We exploit the flexibility of two-photon direct laser writing to optimize a highly versatile fabrication strategy based on a shell-writing procedure with the aim to reduce fabrication time of big inlet/outlet sections compatible with most microfluidic systems for lab-on-chip. Compared with standard microfabrication techniques, requiring several technological steps to obtain suspended hollow structures, this method allows to fabricate complex SMR sensors in only one fabrication step by virtue of its intrinsically 3-D nature. The realized resonant structure was characterized by laser doppler vibrometry, showing good agreement with finite-element methods simulations and an experimental quality factor of the fundamental mode of ~60.

3D printable light-responsive polymers

New photo-curable polymers for 3D printing are provided, exhibiting mechanical light-responsivity upon laser irradiation. Azobenzene moieties are employed both as dyes in the 3D printing process and as active groups providing the desired light responsivity. The incorporation of azobenzene units into polymeric matrices allows a reversible and controllable change of the Youngs modulus of a crosslinked micrometric structure. Depending on the temperature of operation, laser irradiation induces either a decrease (photo-softening) or an increase (photo-hardening) of the Youngs modulus. Such a behaviour can be spatially controlled in order to locally modify the mechanical features of 3D printed objects such as microcantilevers.

Ionic liquid-enhanced soft resistive switching devices

Resistive switching phenomena are of paramount importance in the area of memory devices. In the present study, we have fabricated a simple resistive switching device using a solution processable nanocomposite based on silver nitrate and poly(vinylidene fluoride-hexafluoropropylene). The change in resistance is ascribed to an initial ionic conduction, followed by a non-continuous field induced filament formation. The switching device fabricated with the above-mentioned active matrix displayed a volatile switching behavior. The addition of room temperature ionic liquid plays a fundamental role in triggering permanent memory and reducing the set voltage range up to ten-fold. The change in switching behavior with respect to the applied voltage bias and compliance level set during electrical characterization was studied thoroughly. The present work also gives a glimpse into the importance of device architecture on resistive switching phenomena.

Low-temperature atomic layer deposition of TiO2 thin layers for the processing of memristive devices

Atomic layer deposition (ALD) represents one of the most fundamental techniques capable of satisfying the strict technological requirements imposed by the rapidly evolving electronic components industry. The actual scaling trend is rapidly leading to the fabrication of nanoscaled devices able to overcome limits of the present microelectronic technology, of which the memristor is one of the principal candidates. Since their development in 2008, TiO2 thin film memristors have been identified as the future technology for resistive random access memories because of their numerous advantages in producing dense, low power-consuming, three-dimensional memory stacks. The typical features of ALD, such as self-limiting and conformal deposition without line-of-sight requirements, are strong assets for fabricating these nanosized devices. This work focuses on the realization of memristors based on low-temperature ALD TiO2 thin films. In this process, the oxide layer was directly grown on a polymeric photoresist, thus...

Surface area enhancement by mesoporous silica deposition on microcantilever sensors for small molecule detection

We demonstrate here an easy and controlled technique to enhance the surface active area via highly porous inorganic nanostructure growth on the surface of a microcantilever. A dip-coating approach was used to deposit a continuous mesoporous silica thin film with an accessible pore size of around 8 nm. Both dynamic and static characterizations were performed showing a sensitivity enhancement to relative humidity up to two orders of magnitude with respect to bare cantilevers. The combination of the two analyses gave the possibility to link the adsorption kinetics to the direct quantification of the adsorbed layer mass. These results obtained with water molecules as test analyte pave the way to the use of these composite systems as improved mass and chemical detectors of other small target molecules.

Field localization and enhanced second-harmonic generation in silicon based microcavities

High-quality amorphous Silicon Nitride (a-Si(1-x)N(x):H) Fabry-Pérot microcavities can show resonant surface Second Harmonic Generation (SHG) effect. We consider two different layouts of planar microcavities with almost identical linear reflectance and show how the structure geometry can strongly affect SHG yield. In particular, a difference of more than one order of magnitude in the SHG intensity is observed when the fundamental beam is tuned at the cavity resonance frequency. We explain this finding on the basis of a theoretical model taking into account the spatial distribution of the electric fields of the pump and harmonic frequencies inside the structure. A satisfactory matching of experimental data with the theoretical model is obtained by considering the source of second-order nonlinearity as limited to surface contributions.